What is relay protection and what is it for?

What is it used for?

First of all, let's talk about why you need to use RZA.The fact is that there is such a danger as the occurrence of a fault current in the circuit. As a result of short-circuit, conductive parts, insulators and equipment itself very quickly collapse, which entails not only the occurrence of an accident, but also an accident at work.

In addition to a short circuit, overvoltage, current leakage, gas evolution during oil decomposition inside the transformer, etc. can occur. In order to detect the danger in time and prevent it, special relays are used which signal( if a malfunction in the operation of the equipment does not pose a threat) or immediately turn off the power in the faulty section. This is the main purpose of relay protection and automation.

Basic requirements for safety devices

So, in relation to the RZA, the following requirements are met:

1. Selectivity. In the event of an emergency, only the area on which an abnormal operating mode is detected should be disconnected. The rest of the electrical equipment should work.
2. Sensitivity. The relay protection must respond even to the lowest alarm values ​​(set by the pick-up value).
3. Speed. No less important requirement for the RZA, t. The faster the relay will work, the less chance of damage to electrical equipment, as well as the occurrence of a hazard.
4. Reliability. Of course, the devices must perform their protective functions in the specified operating conditions.

In simple words, the purpose of relay protection and the requirements imposed on it are that devices must monitor the operation of electrical equipment, react promptly to changes in the operating mode, instantly turn off the damaged section of the network and signal personnel about the accident.

Relay classification

In considering this topic, one can not help but mention the types of relay protection. The classification of the relay is as follows:

• Connection method: primary( connected directly to the equipment chain) and secondary( connection via transformers).
• Variant of execution: electromechanical( the system of movable contacts disengages the circuit) and electronic( disconnection occurs by means of electronics).
• Purpose: measuring( measure voltage, current, temperature and other parameters) and logical( send commands to other devices, time delay, etc.).
• Method of action: direct protection relay( mechanically connected to the tripping device) and indirect action( control of the electromagnet circuit, which turns off the power).

As for the types of relay protection devices themselves, there are a lot of them. Immediately consider what kinds of relay are and what they are used for.

1. The overcurrent protection( overcurrent protection) works if the current reaches the setpoint set by the manufacturer.
2. Directional overcurrent protection, in addition to the setpoint, the direction of power is monitored.
3. Gas protection( GZ), is used to disconnect the power of the transformer as a result of gas evolution.
4. Differential, field of application - protection of busbars, transformers, and generators by comparing the values ​​of the currents at the input and output. If the difference is greater than the setpoint, the relay protection is activated.
5. Remote( DZ), turns off the power if it detects a decrease in the resistance in the circuit, which occurs if a short-circuit current occurs.
6. Remote protection with high-frequency interlock, used to disable the overhead line when a short circuit is detected.
7. Remote with optical lock, a more reliable version of the previous type of protection. The effect of electrical noise on the optical channel is not so significant.
8. Logical busbar protection( LZH), also used to detect short circuit, only in this case on buses and feeders( supply lines departing from the substation buses).
9. Arc. The purpose is to protect complete switchgears( KRU) and complete transformer substations( KTP) from fire. The principle of operation is based on the operation of optical sensors as a result of increased illumination, as well as pressure sensors with increasing pressure.
10. Differential-phase( DFZ).They are used to control the phases at the two ends of the supply line. If the current exceeds the setpoint, the relay trips.

Separately, I would also like to consider the types of electroautomatics, the purpose of which, contrary to relay protection, is to turn the power back on. So, in modern RZA use automation of the following form:

1. Automatic input of reserve( AVR).This automation is often used when connecting the generator to the network, as a backup source of electricity.
2. Automatic reclosing( automatic reclosing).Scope of application - power lines with a voltage of 1 kV and above, as well as substations, electric motors and transformers.
3. Automatic frequency unloading, which disconnects third-party devices when the frequency decreases in the network.

In addition, there are the following types of automation:

Here we have considered the purpose and scope of relay protection. The last thing I'd like to talk about is what the RZA consists of.

Relay protection

The relay protection device is a circuit of the following parts:

1. Starting devices - voltage, current, power relay. Are intended for the control of an operating mode of an electric equipment, and also detection of disturbances in a chain.
2. Measuring elements - can also be located in the starting organs( current, voltage relay).The main purpose - the launch of other devices, the signal as a result of the detection of abnormal operating mode, as well as instantaneous disconnection of the devices or with a delay in time.
3. Logical part. It is represented by timers, as well as intermediate and indicator relays.
4. Executive. It is responsible immediately for switching off or switching on the switching devices.
5. Transmitting part. Can be used in differential-phase protection.

Finally, we recommend that you review a useful video on the topic:

This and all that we wanted to tell you about the purpose of relay protection and the requirements imposed on it. We hope that you now know what RPA is, what its scope is and what it consists of.

It will be useful to read:

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